The principal tensor values for thermal deformations in acmite, diopside, hedenbergite, jadeite, spodumene, and ureyite, have been calculated from published experimental data. The direction of maximum extension of all these minerals is the b axis; the direction of minimum extension does not, usually coincide with the axis of the pyroxene chains (c), but is correlated with the degree of anisotropy of deformations of the monoclinic plane (ae) (010) and the rate of change in beta with T. The calcic pyroxenes display a markedly anisotropic character in the deformations up to the point of negative extension along certain directions, whereas the alkaline pyroxenes are less anisotropic. In this respect, it is suggested that the calcic clinopyroxenes contribute in a greater degree to rock decompression under conditions of metamorphism than do the alkali clinopyroxenes.-D.A.B.